Self-locking electrical plug and socket



H. J. MODREY 2,427,297

LOCKING ELECTRICAL PLUG AND SOdKET FiledJulj 10, 1944 Sept 9, 1947. 1

SELIF 4 Sheets-Sheet 1 p 1947- H. J. MODREY 2,427,297

SELF-LOCKING ELECTRICAL PLUG AND SOCKET Filed July 10, 1944 4 Sheetsheet 2 02) FF??- 4 [WE A llorneya'.

Sept 9, 1947.

H. J. MODREY SELF-LOCKING ELECTRICAL PLUG AND SOCKET Filed July 10, 1944 4 Sheets-Sheet s In venlor:

4 9,4 A Ilorneys.

Sept. 9, 1947. H. J. MODREY SELF-LOCKING ELECTRICAL PLUG AND SOCKET Filed Ju1y 10, 1944 4 Sheets-Sheet 4 Patented Sept. 9, 1947 SELF-LOCKING ELECTRICAL PLUG AND SOCKET Henry John Modrey, London, England, assignor to Modrey Patents Corporation, Essex-County, N. J a corporation of New Jersey Application July 10, 1944, Serial No. 544,188

1 '23 Claims.

This invention relates to self-locking electrical plugs andsockets wherein locked conducting engagement of the plug to the socket is efiected by the insertion of the plug in the socket.

The basic principle upon which plugs and sockets with which the present invention is concerned operate is disclosed in my previous patent application U. S. Patent Oflice Serial No. 487,761, now Patent No. 2,423,250, issued July 1, 1947. The primary object of my present invention is to apply the said basic principle to standard systems of flat-pin outlet plugs and sockets.

A further object of my invention is to provide a plug of this flat-pin type that may readily be locked into its socket in order to prevent its be ing withdrawn when pull is exerted upon the plug or upon the cord or cable which is attached to the plug.

A further object is to provide an outlet plug that locks itself to its socket in the fully closed,

shock proof and so lends itself to use in aircraft,"

railroad cars, automobiles, tanks, tractors, and other appliances which are subject to vibration.

A further object is to provide electrical outlet plugs and sockets with lower and more constant contact resistance and generally improved electrical contact qualities, by combiningthe selflocking mechanism with the contact parts and thus providing spring-tensioned interlocked contact, in addition to the customary frictional contact between plug and socket contacts.

A further object is to provide a plug which upon insertion into its socket, is capable of supporting the weight of electrical appliances such as lighting fixtures or portable tools.

A further object is to provide a plug and socket suitable for overhead wiring, viz., for the pro- ,vision of semi-permanent electrical connections between electrical appliances and a plurality of socket outlets mounted overhead or carried on bps bars or conduit tubes.

A further object is to provide a plug suited for fire alarm or burglar alarm installations that, once inserted cannot be removed from its socket unless access is had to the underside or inside of the socket.

A still further important object of my inven- .tion is to provide for interchangeability between i 2 invention, in that socket outlets according to my invention will receive such standard plugs, and plugs according to my invention will fit into such standard socket outlets. It is of course understood that self-locking action will result only from the conjoint use of plugs and sockets according to my invention.

The invention will be clearly understood on reference to the accompanying drawings which form part of the specification:

Figure l is a perspective view of the plug contact blade with the locking mechanism attached;

Figure 2 is a perspective view of the socket contact containing the said opening or slot;

Figure 3 is a perspective view of the two aforementioned components in locked conducting enagement;

Figures 4, 5, 6, 7 are sectional views of the contact blade, the locking mechanism, and part of the socket contact, in progressive stages of looking engagement; V

Figures 8, 9 are part-sectional views of a plastic twin-pole plug;

Figures 10, 11 are part-sectional views of a twin-pole plug made from rubber;

Figures 12, 13 show a plan view and a sectional view respectively of a twin-pole socket;

Figure 14 is 'a part-sectional view of a twinpole plug of a spring-less type, made from rubber;

Figures 150. and 15b show details of the locking mechanism employed in the plug shown in Figure 14; a

Figure 16 isa perspective view of a five-pole p a Figure 17 is a plan view of the corresponding socket outlet;

Figure 18 is a perspective view of a circular five-pole plug;

Figure 19 is a plan view of .the corresponding socket outlet;

Figure 19a is an elevational side view of a connected plug and socket according to Figs. 18 and 19 respectively.

Figures 20a and 2011 show details ofa compensating socket contact, used as a centre contact in the socket outlet shown in Figure 19;

Figure 21 is a part-sectional view of an ap- The plug contact blade shown in Figure 1 con sists of a stem i terminating in an enlarged blade contact 2. The locking slide d is held in slidable engagement with the stem 1 by the slide ring 5, and is spring influenced axially between the blade contact by a spring 8 which bears against the head M of the locking slide 5, and against the corner Ia of the stem B respectively. 3 indicates a hole to which a conducting wire or a terminal screw may be ailixed.

Referring to Figure 2, which illustrates the socket contact, the length of the rectangular slot ii in the top part I of the socket contact corresponds to the width of the blade contact 2, at its widest part. The cross sectional width of the slot 8 may conveniently exceed that of the thickness of the blade, so as to permit access to blades .eral applies to the mechanism of all the various form of plugs and socket described hereinafter.

Blade 2 is entered into the slot 8, Figure 4 showing the position immediately before the entry. Towards the end of its travel, the locking slide l bears against the surface l of the socket contact. Slot 8 being substantially filled as to its larger dimension by blade 2, the slide 6 is thus pushed backwards axially, compressing the spring 8, as shown in Figure 5. As soon as the slope 2a which connects the stem 8 with the enlarged blade 2, is reached, blade 2 is displaced sideways so that the spring-influenced locking slide t snaps into the slot 8, as shown in Figures 6 and 3.

The stem I together with the locking slide d now fills substantially the slot 8 and, as a result, the enlarged blade 2 underlies the underside of the slot 8 by the displacement width of the locking slide d. It, will be obvious that pull at the stem I cannot remove blade 2 as the joint width of the parts now situate below slot 8, considerably exceeds the length of the slot, and in consequence the locking action of the mechanism is mechanically positive, and not frictional or dependent on spring pressure. Electrical contact is established by the blade 2 entering in between back plate 9 and tongue iii of the socket contact, and is supplemented by the locking mechanism engaging the socket contact under spring influence.

Figure 7 shows the unlocking action. The locking slide it has been lifted clear of slot 8, against the pressure of spring 8. Once this position of the locking slide relative to the slot 8 is reached, blade 2 is at liberty to slide sideways under the cam action of the slope 2a, and can thereafter be withdrawn through the slot 9.

To sum up, the blade is locked automatically by the inserting push, and removed automatically by pull applied to the locking slide. The various I forms of plugs and sockets hereafter described, embody various means of applying these two actions.

The whole of the foregoing description must be understood as referring to relative movements of the various parts, as the locking principle according to my invention applies also to a mechanical reversal of the mechanism or the order of operation. For instance, Figures 21 and 22 show a plug and socket respectively in which self-locking is effected not by insertion of the plug, but by movement of the socket relative, to the stationary plug.

Figures 8, 9, 10 and 11 show twin-pole plugs embodying the invention. In Figures 8 and 9 two blades and locking slides are contained in a housing of plastic or the like insulating material.

This housing it has in its bottom two slots l9 which serve to replace the functions of the missing slide or collar 5, by holding the locking slides i and the stems l in slidable engagement. The top portion of the plug consists of two parts it and i5 which are connected by a holding screw it, once the cord or cabl I! has been wired to the terminal screws 3a. Parts i l and i5 conjointly are so shaped as to slide inside the bore of the housing it. The inside of the two parts Hi and it contains recesses such as shown in like which ensure that both parts are firmly joined to the terminal portion of both stems i once the connecting screw it has been fastened.

Figures 12 and 13 show the corresponding socket outlet which contains two socket contacts as shown in Figure 2. The lugs la and lb shown in Figures 2 and 13, serve to amx the socket contacts to the insulating socket top plate which may be a plastic moulding. The top plate 241 has a slightly recessed portion 25, corresponding in shape to that of the bottom of a. plug. Two slots 26 disclose the locking slots 8 in the two socket contacts. Afllxed to the socket contacts are two terminal screws 21! and 28.

The socket outlet as described is identical for all twin-pole plugs described herein. It will be obvious that the outlet will also co-operate in the customary manner with any standard twin-pole plug, the blades entering through the clearance slots 26 and the slots 8 in between the socket contacts where they are held between the back plates 9 and the tongue to. It will further be obvious that the tongue ill is not essential for the functioning of the socket contact, the provision of an appropriately shaped slot 8, in conjunction with a socket contact of suitable shape, being all that is necessary to establish good electrical connecion.

If any twin-pole plug according to my invention is inserted into the socket outlet shown in Figures 12 and 13, by pressing on the top part lt-ld of the plug, the locking mechanism on both blades will engage in its corresponding slot 8, as previously described with reference to Figures 4-6. Subsequent pull at the cord or cable cannot dislodge the plug, short of shearing blade 2 through a slot of considerably smaller cross section.

The plug can only be removed by pull at the bottom housing I8, when the locking slide t is lifted clear off the slot 8, as shown and described with reference to Figure 7. Parts l8 and It-lfi slide freely inside each other, and it will be obvious that pull at the cord or cable i1 is not transmitted to the housing It.

The amount of telescoping movement required for the operation of the locking mechanism, is indicated in Figures 8 and 9 by means of dotted lines. For convenience of operation, it is desirable to keep this operating stroke as small as possible. The operative position of thelocking mechanism is reached when the slope 2a is pro,- Jected slightly beyond the tip of the locking slide 48, and the required operating stroke therefore demechanism ofthe plug cannot, of course, become j pends upon the protruding length of locking slide 4.

On the other hand, I, there is a certain danger that a rocking or sideways motion applied to the inserted plug may nroiect the end of locking slide 4 longitudinally out of its locking slot I, in which case the locking mechanism would disengage. It is therefore essential to hold the plug forcibly in an upright position, relative to its socket.

To a certain extent, the plug is so steadied by the shaped recess 2! in socket plate 24, as shown in Fig. 12. The depth of this recesshowever should not exceed the protruding length of the locking slide 4. in view of the slight zigzag movement occurring during the insertion of the plug when blades 2 jump via their. slopes in from an axially symmetrical position into locked position. This limitation as to depth, limits the usefulness of the said recess for steadying purposes.

It is not convenient to use for such steadying purposes the means customarily applied to standard plugs and sockets, viz., provision of indentions or holes in the blades, and of corresponding raised portions in the socket contacts. It is evident from Figs. 4 to 6 that, owing to the sideways displacement occurring during the locking motion, the blade comes to rest in a position which is unsymmetrical in relation to the true axis of the socket contact. If therefore the described customary means for steadying the plug blades were employed, the said raised portions would have to be in unsymmetrical positions on the socket contacts, and as a result the plug could only be inserted in one given position. As indiscriminate insertion is the more common requirement for outlet plugs, positive steadying of the plugs against the socket is achieved by the following means:

At the side of the contact back plate 8. the two bent lugs I l and I! are provided, as shown in Figs. 2 and 3. The back plate 9 is of such width that the side of blade 2, after insertion, is flush with one side of the back plate 9, whichever way the blade is inserted. In Ifigure 3, lug ll therefore makes it impossible for blade 2 to move sideways on this side.

By arranging two contacts within one socket outlet to be fixed in opposite directions, as shown in Fig. 13, both lugs II and I! on opposite sides of the two back plates 9 in the two contacts, come into play and conjointly prevent any movement of the blades 2. These lugs aflord a positive holding device, irrespective of the shape of the plug housing, and independent of the position of the plug.

It will be obvious that a plug according to my invention may be used in conjunction with an appropriate standard socket. The blades 2 will enter a standard socket contact, and with most types of standard socket, the relative movement between blades and locking slides will'assist in inserting the plug to its full depth. In the absence of locking slots in the socket outlet, the locking operative.

Whilst Figs. 8 and 9 show a plug made from plastic or the like insulating material, Figs. 10 and 11 show another twin-pole plug for cooperamade from rubber or the like elastic material.

-As described with reference to Figs. 8 and 9, p

the plastic plug requires for locking and unlocking a slight telescoping movement between its top with a short locking slide 6 ing to Figs. 10 and ii, the necessity for providing.

separate telescoping parts has been eliminated,

. by providing an elastic housing capable of iongitudinal compression which affords the required longitudinal movement.

' blades with attached locking mechanism are ntained in the rubber housing Ill-2 I which is shown to consist of two symmetrical halves to be Joined together after the cord or cable I! has been connected to the terminal screws to. The top parts of both in and I l contain shaped recesses Ila which insure that once the two halves ll and II have been joined together, the said top parts conlointly are firmly connected to the terminal portions of both blade stems I. The slide rings I are embedded and held in the thick bottom portion of the Joined rubber housing.

If the plug is inserted into a socket as shown in Figs. 12 and 13, and for this purpose is pushed in by the grooved .top part 22 (marked "In) the plug which rests on the socket top plate will be compressed as indicated by the dotted lines, until operative position of blades 2 relative to the looking slides 4 (likewise indicated by dotted lines) is reached. when the locking mechanism engages. The plug is again impervious to pull at the cable, but may be removed by pull at the grooved bottom part 23 (marked "Out), or alternatively by holding the plug at it and depressing top part 2!. Either action will bring the locking mechanism into operative position as shown in Fig. 7. Internal rubber buffers may be employed to stiii'en the housing and to prevent undue compression of the housing during insertion or removal.

- Fig. 14 shows a simplified type of twin-pole plug made-from rubber or other elastic material, in which the inherent elasticity of the housing material is utilised to replace the operating spring 6. The plug shown by way of example is of the 40 type wherein the cover of the appliances cord or cable is moulded integrally with the plug body. The spring 6 operated so as to push the looking slide 4 and the slide" ring 5 constantly towards blade 2. This action is replaced by the inherent elasticity of the rubber housing 28 and BI, which may be increased by an appropriate arrangement of internal ribs 88a, b, c, d which favours easy compression of the housing, but at the same time limits the stroke.

However., another function of spring s was to hold. locking slide e in its position inside the slide tion with the socket shown in F188. 12 and 13,

ring 5, by means of pressure on the slide head do. in the absence of a spring this action must be compensated by fastening lochng slide t permanently to slide ring a, for example by means of a pin or rivet 32 as shown in Fig. 15. The locking slide 6 then participates in the spring tension imparted to slide ring 5 by the elastic housing, and the plug functions and is inserted and removed as described with reference to Figs. 10 and 11.

Apart from the obvious simplification in design, springless elastic plugs according to my invention oller electrical advantages for use in ultra-high frequency circuits in which operating spring 6, although small and short-circuited, may conceivably set up disturbances. For the identical reason, springless plugs ofier electrical advantages for use in co-axial connectors.

Fig. 16 shows a multi-pole plug containing by way of example five flat-pin contacts in line. In a plug of this description it is not necessary for eflective looking, to attach a locking mechanism to each contact blade, unless of course this'is and bottom portions. In the rubber plug accordto desirable on electrical grounds. on the plus shown in Fig. 16, locking slides 4 have been added only to the two end blades, whilst the three centre blades 35a, b, c are without such locking mechanism. All blades are anchored in the top part 34 of the plug which is capable of telescoping movement inside the housing 33, as described with reference to the twin-pole plu shown in Figs. 8 and 9. Access to the terminals may be had by removing the top plate36 which also releases the cord or cable from the cable gland 31. The plug is inserted and locked by pressure upon its top 34-38, and is removed by pull at the housing 33, or by compressing the top 3436 relative to the housing 33.

It is not advantageous to fasten the non-locking blades 350., b, c to the housing 33, as in this case the telescoping movement between the two plug parts 33 and 34 would be taken up by the wires in the cord or cable H which are firmly clamped into the cable gland 31, but would have to follow the terminals attached to 35a, 17, c on their downward move, with the result that breakages are likely to occur after some time. It is more advantageous to have stationary terminals and to let the auxiliary blades participate in the slight movement imparted to the "locking blades during locking and unlocking.

Fig. 17 shows the arrangement of the corresponding socket which is equivalent, except for the number of contacts provided, to the socket shown in Figs. 12 and 13, although the three centre contacts may be constructed Without the locking slots.

However, in the construction of the three centre socket contacts or of the corresponding blades 35a, b, c, the sideways displacement movement occurring during insertion of the plug must be taken into account. narrower contact blades have been provided so as to prevent jamming whilst this zigzag movement occurs.

Fig. 18 shows a circular -pole plug in which only the centre blade 2 carries a locking slide 4. Fig. 19 shows the arrangement of the corresponding socket. In this construction, the zigzag or displacement movement occurring at the centre blade Zduring the locking motion (shown in Figs. 5 and 6) would prima facie make oper-' ation impossible, as the permissible motion of the plug is limited by the four non-locking blades 39a, b, c, d which once inserted permit only of a straight rectilinear movement. Moreover, plugs of this kind are usually inserted into their sockets to a considerable depth, and are thus fur ther guided by the socket opening which permits only of a straight downwards motion. It is impossible, in this instance, to apply the means In the instance of Fig. 16,

indicated in Figs. 16 and 17, viz., narrower nonlocking blades, as all blade-receiving slots point into different directions whilst the displacement movement occurs in the lengthwise direction of the central or locking slot 48.

In a plug of this type (or in other cases where the displacement movement interferes with the proposed operation of the plug), the displacement movement must be compensated. The

and through the clearance slot 50 enters in between the contact tongues 49a and b. Once'blacle 2 has reached the position shown in Fig. 5 (the locking slide 41 being substituted for the top part 1 shown in Fig. 5), the locking slide 4 enters the locking slot 68, at the sam time displacing the movable locking slide 41 sideways, as required.

This displacement compensation inside the socket contact enables plugs and sockets to be joined and parted by means of a straight rectilinear movement, so that the relative angular position of non-locking blades as shown in Fig. 18, as well as their width does not interfere with the proper functioning of the connector. It will be obvious that if displacement is compensated as aforesaid, pin type auxiliary plug contacts may be employed, cooperating with tubular contacts within the socket.

The plu shown in Fig. 18 corresponds to the one shown in Fig, 16, in that both blade 2 and the auxiliary or non-locking blades are anchored to the telescoping top part M, whilst access to all terminals is had by unscrewing part 62.. The plug is inserted by pushing it into the socket by pressure on part 42, and is removed by pulling at the knurled portion of the housing as which again serves to lift the locking slide 5 until the plug disengages.

In view of the foregoing, the construction and function of the socket according to Fig. 19 will be self-explanatory. Socket contacts tea, 1?, c. it may obviously be standard socket contacts. as a result of displacement compensation, the socket cover 45 may be located considerably below the flange 43 of the socket, as long as the knurled portion of the plug body Ml protrudes sufieiently to afford a grip.

If the insertion depth is increased to such an extent that no part of housing 4t protrudes, the plug may be locked in its socket as described. but cannot be removed or withdrawn without dismantling the socket, or lifting the locking slide 4 from the underside of the socket by means of an instrument. A plug embodying this feature ma be used for purposes where it is undesirable to have the plug removed once it has been inserted, such as, for example, in burglar or fire alarm installations.

Fig. 19a shows the plug of Fig. 18 applied to the socket of-Fig. 19. As will be noted, cover plate 45 of the socket is recessed to form a cupshaped portion 43a which receives plug body 48. As will be apparent, plug body 411' is not accessible after being pressed home. As a result, the connector elements can not be separated without access to the underside of the socket or a, special instrument. The insertion of the plug body into a recess of the socket has also the advantage that the connector presents a continuous surface of insulation material, thereby avoiding the daner of short circuits or shocks. For the latter purpose, of course, it will not be necessary to recess the socket so deeply that the plug body is entirely concealed.

Fig. 21 shows an appliances plug according to my invention, viz., a plug for incorporation with domestic and like electrical appliances, to be connected to a current-carrying socket which is aflixed to a cord or Wire, as shown in Fig. 22.

The top or terminal part of the two blade stems l is aflixed to an insulating housing 5|, through the bottom of which the terminal screws 3:; protrude, for connecting inside the electrical appliance. The flange 51a is aflixed to the said appliance, and the telescoping inner housing 52 which carries two slide rings guiding blades 2 and locking slides 4, protrudes slightly from theflange 5|a. f The line Socket shown in Fig. 22 may b made from plastic, rubber or other insulating mate- ,rial, and embodies two of the socket contacts shown in Fig. 2, duly positioned and separated by recesses and a central Wedge or separator 54a in the housing 54. Access to the locking slots 8 is'had through the clearance slots 55 in the housing.

I: the socket with its two locking slots 8 is" pushed over the two plug blades 2, the locking slides 4 are lifted and the locking mechanism functions asshown in Figs. .5 and 6, but with the distinction that in this instance the blades are held stationary whilst the locking slots 8 are moved upwards, until both locking slides are free to snap into their locking slots 8.

To remove the line socket, it is again necessary to lift the locking slides 4 clear off their respective locking slots 8. The required relative movement between the two blades 2 and their locking slides 4 in this application of my invention, is effected by depressing the knurled rim 53 of the inner housing 52 (as shown in dotted lines) until the locking slides 4 are free, when the line socket can be withdrawn.

The description of various electrical outlet Plugs and sockets according to my invention, shows that the basic fiat-pin locking mechanism described therein, may be incorporated within various forms of electrical outlet plugs and sockets. The displacement-compensation socket contact shown in Figs. 20a and 20b, serves to remove constructional limitations originally inherent in the locking mechanism. The range of connectors described is by way of example only, whilst it will be obvious that various permutations or adaptations of the basic self locking mechanism as apdental or deliberate cable pull, and to the effects it of severe shock or vibration. The locking strength is independent of the operating spring employed, but is equivalent tothe shearing strength of the contact blade in its socket hole. For this reason,the plug is capable of supporting considerable weight such as lightin fixtures or portable tools, and may therefore conveniently be employed for overhead or bus-bar wiring in factories, or for the installation of quickly removable lighting fixtures such, as fluorescent lamps, inspection lamps, lighting fixtures in showrooms, or the like.

Moreover, the contact parts themselves in plugv and socket respectively, form the. locking mecha- Once the plug has been inserted, the custqmary friction contact between blade and socket contact is established, but in addition hereto contact blade and socket contact are mechanically interlocked and under constant spring tenplied to plugs and sockets,' may be constructed on the .springiness of the socket tongues which tends to decrease with continued use. The applied spring-tension makes this interlocking electrical contact eminently suitable to withstand vibration and shock, without change in contact resistance.

Lastly, electrical plug and socket outlets according to my invention look only when inserted to full depth. That is to say, once inserted, there cannot be any gap between plug and socket in which current-carrying parts are exposed, as is the case with half-opened standard plugs and sockets. This safety feature can be further enhanced by providing an operating spring which it is impossible for a child to compress so as to unlock the plug, whilst it can be easily handled by an adult person.

It will be'clear from the foregoing that, broadly stated, my invention involves the provision of a locking mechanism affixed to or acting in association with the contact blade or blades of a fiat.- pin plug. If the locking blade--which may or may not be a current carrying element-is inserted in an opening or slot, the said locking mechanism becomes operative during the process of insertion. During the final movement of insertion, a recessed portion of the blade enters the slot, and this reduced width of the blade allows the spring-tensioned locking slide to snap into the said slot, alongside the blade. The nonrecessed wider front part of the blade now overhangs the slot and remains locked therein, until the locking slide is lifted or withdrawn from the slot.

What I claim and desire to secure by Letters Patent is:

1. In an electrical plug connector 2. contact socket including a locking plate having a slot therein, a cooperating locking device comprising a fiat blade having its forward end of width designed for insertion through said slot, said blade being cut away on one side to form a stem of lesser width than that of the forward end of the blade and thus to provide a locking shoulder at the top of said forward end, a locking slide slidable within limits along the uncut edge of the blade, the efiective part of said locking slide being of a width substantially equal to the width of the portions cut-away from the opposite edge, means to hold the locking slide in slidable engagement with the edge of the blade and to impose a limit on its forward movement, and yieldable means tending to maintain saidlocking slide in its forward position.

2. In an electrical plug a locking device according to claim 1, wherein the means for hold- .ing the locking slide in slidable engagement with v the blade and limiting its forward movement is constituted by a slotted guide.

3. In an electrical plug a locking device according to claim 1, wherein the means for holding the looking slide in slidable engagement with the blade and limiting its forward movement is constituted bya slotted guide positively secured in the bottom of a casing containing the stem of the blade.

4. In an electrical plug a locking device according to claim 1, wherein the means for holding the locking slide in slidable engagement with the blade and limiting its forward movement is constituted by a slotted guide positively secured in the bottom of a casing containing the stem of the blade, and the locking slide is positively connected to the slotted guide.

5. In an electrical .plug a locking device according to claim 1, wherein the means for holding the locking slide in slidable engagement with the blad and limiting its forward movement is constituted by the slotted end of a casing housing the stem of the blade.

6. In an electrical plug connector a contact socket including a locking plate having a slot therein, a cooperating locking device comprising a flat blade having its forward end of width designed for insertion through said slot, said blade being cut away on one side to form a stem of lesser width than that of the forward end of the blade and thus to provide a locking shoulder at the top of said forward end, a locking slide slidable within limits along the uncut edge of the blade of a width substantially equal to the width of the portion cut away from the opposite edge, a guide beyond which the forward wider end of the blade projects and through which the forward effective part of said locking slide passes, and yieldable meansacting on the locking slide,

' whereby on passage of the wider forward part of the blade into and through the slot in the locking plate of the socket the locking slide is moved relatively to the blade against the yieldable means until the wider forward part of the blade has passed through the slot in the locking Plate whereupon the forward end of the locking slide is freed for projection into the slot in the socket locking plate alongside the narrower stem of the blade, and thereby displaces the blade sideways to secure the locking shoulder in locked engagement beneath the underside of the locking plate.

7. An electrical plug comprising a flat blade having its contact making forward end of normal width for insertion into co-operating engagement with a flat-pin socket contact said blade being cut away on one side to form a stem of lesser width than that of the contact making forward end and thus to provide a locking shoulder at the top of said contact making forward end, a locking slide slidable within limits along the uncut edge of the blade of a width equal to the width of the portion cut away from the opposite edge, a'guide beyond which the forward contact making end of the head projectsand through which the forward part of said lockin slide passes, yieldable means acting on the locking slide, and means to limit the forward movement of the locking slide under the influence of the yieldable means, whereby on passage of the wider contact makingpart of the blade into and through a slot in the socket plate the locking slide is moved relatively to the blade against the yieldable means until the wider contact making part of the blade has passed through the slot in the socket plate whereupon the forward end of the locking slide is freed for projection into the slot in the socket alongside the narrower stem of the blade, to displace the blade sideways and thus secure the locking shoulder in looking position beneath the underside of the socket plate.

8. An electrical plug comprising a flat blade having its contact makin forward end of normal width for insertion into co-operating engagement with a flat-pin socket contact said blade being cut away on one side to form" a stem of lesser width than that of the contact making forward end and thus to provide a locking shoulder at the top of said contact making forward end, a headed locking slide slidable within l t along the uncut edge of the blade of a width equal to the width of the portion cut away from the opposite edge, a guide beyond which the blade against the spring means until the wider contact making part of the blade has passed through the slot in the socket plate whereupon the forward end of the locking slide is freed for projection into the slot in the socket alongside the narrower stem or the blade, thereby to displace the blade sideways and .thus secure the locking shoulder in locked engagement beneath the underside of the socket plate.

9. An electrical plug comprising a terminal block, a flat blade connected to said block and having it contact making forward end of normal width for insertion through the slot of a co-operating flat-pin contact socket, said blade being cut away on one side to form a stem of lesser width than that of the contact making forward end and thus to provide a lockin shoulder at the top of said contact making forward end, a housing through which the stem passes with relation to which the terminal block can telescope, a headed locking slide slidable along the uncut edge of the blade of a width substantially equal to the width of the portion cut away from the opposite edge, a'guide slot in the lower end of the housing beyond which the forward contact making end of the head projects and through which the operative part of said locking slide passes, the part of the bottom'end of the housing bordering the slot therein co-operating with the head of the locking slide to limit both the forward movement of said locking slide and the rearward movement of the blade, and a spring surrounding the stem of the blade and acting on the locking slide, whereby on passage of the wider contact making part of the blade into and through the slot in the socket plate the locking slide is moved relatively to the blade against the influence, of the spring until the wider contact making part of the blade has passed through the slot in the socket plate whereupon the forward end of the locking slide on projection into the slot in the socket alongside the narrower stem part of the blade displaces the blade sideways and thus secures the locking shoulder in locked engagement beneath the underside of the socket plate.

10. An electrical plug according to claim 8, wherein a pair of the contact making blades and locking mechanisms are arranged side by side in a common housing to form a twin pole plug.

1 11'. An electrical plug connector according to claim 1, wherein the socket is provided with. a cup-shaped insulation portion, and wherein the plug is adapted to lock in the socket only when the contact making parts of the plug have been inserted sufiiciently far into the cup-shaped portion of the co-operating socketthat they are enclosed and shielded against outside contact by the insulation of said portion.

, 12. An electrical plug according to claim 7, wherein the yieldable means is constituted by the resilience of the housing.

13. An electrical plug having a locking mechanism according to claim 1 and additional current Carrying blades.

answer 13 a 14. An electrical plug having locking mechanism according to claim 1, wherein a locking blade and its locking mechanism is situated centrally oi the plug and current carrying contact blades are arranged around it.

15. An electrical plug having locking mechanism according to claim 1, wherein a locking blade centrally oi the plug and current carrying contact blades are arranged around it, and the socket has a slidable slotted plate whose movement compensates for the displacement movement of said locking blade.

18. An electrical plug having locking mechanism according to claim 1 wherein the flat blade carries current anda socket contact element comprises a one-piece bent up strip metal member having a back plate with which one face of the current carrying blade of the cooperating ilat pin contact plug makescontact, a resilient tongue with which the other face of the current carrying blade makes contact, and a slotted socket plate joining the back plate'to the tongue.

1'7. An electrical plug having locking mechanism according to claim 1 wherein the flat blade carries current and a socket contact element comprises a one piece bent up strip metal member having a back plate to which electrical connection is made with which one face of the current carrying blade of the flat-pin contact plug makes contact, a resilient tongue diverging at its upper end from said back plate and resiliently connected thereto by a bridge forming the socket plate, a slot in the socket plate designed to receive the current carrying blade of the contact plug and permit it to be inserted and held between the back plate and the free end'of the tongue, and bent over lugs at the sides of the backplate to restrain lateral movement 01 the tongue relative to the back plate. 18. An electrical plug connector having a locking mechanism according to'claim 1 wherein the flat blade is arranged to carry current, and a socket having flat contact elements with which the blade of the flat-pin plug can make contact, and a slotted locking plate so located that when the plug is inserted the contact blade of the plug passes through the slot prior to its reaching the contact element of the socket, whereby when the plug is fully inserted. the locking shoulder of the displaced contact blade becomes locked beneath the locking plate. 7

19. An electrical plug connector having a locking mechanism according to claim l, in combination with a socket having its locking plate located at such a depth that when the plug has been inserted into locked engagement with the socket its removal can only be eflected by destruction or the aid of special tools.

20. An electrical plug connecter comprising a plug member and a socket member including a locking plate having a slot therein, said plug member including a flat blade having a forward contact end designed for insertion into said slot, said blade being cut away on one side to form a stem of lesser width than that of said forward end and to provide a locking shoulder at the top of said forward end, a locking slide slidable within limits alongthe uncut edge of the bladeand a width substantially equal to the width of the portion cut a and its associated locking mechanism is situated pression of the flexible housing into the direction or the stem axis until the wider forward part oi the blade is passed through the slot in the looking platewhereupon the forward end'of the locking slide is freed for projection into the slot in the socket locking plate alongside the narrower stem of the blade, thereby displacing the blade sideways to secure the locking shoulder in locked encontact end designed for insertion into said slot,

said blade being cut away on one sideto form a stem of lesser width than that of said forward end and to provide a locking shoulder at the top of said forward end, a locking slide slidable within limits along the uncut edge of the blade and a width substantially equal to the width of the portion cut away from the opposite edge, a. housing made of flexible material within'which housing the blade and the locking 'slide are disposed, said holising supporting the stem and including a guide slot beyond which the forward wider end of the blade projects and through which the forward effective part of the locking blade passes, and spring means surrounding the stem and acting on the locking slide, whereby,'on passage of the wider forward part of the blade into and through the slot in said locking plate of the socket member, the locking slide is moved relatively to the blade in response to a compression of the spring means and of the flexible housing into the direction of the stem axis until the wider forward part of the blade is passed through the slot in the locking plate whereupon the forward end of the locking slide is freed for projection into the slot in the socket locking plate along side the narrower stem of the blade, thereby displacing the blade sideways to secure the locking shoulder in'locked engagement with the underside of the locking plate.

22. In an electrical plug connector a, contact socket including a contact plate having an openone side to form a stem of away from the opposite edge,-a housing made of ing therein, a laterally slidable locking plate having a slot therein elongated in the direction of the lateral locking plate movement and positioned to be in registry with said opening, the longitudinal length of said slot being shorter than the length of said opening in the direction of the lateral locking plate movement, and a co-operating locking device comprising a flat blade having at its forward end a width designed for insertion throughsaid slot, said blade being cut away on lesser width than that of the forward end of the blade and thus to provide a lockingshoulder at the top of said forward end, a locking slide slidable within limits along the uncut edge of the blade, the 'eifective part of said locking slide being of a width substantially equal to the width of the portions cut-away from the opposite edge, means to hold the locking slide in slidable engagement with the edge of the blade and to impose a limit on its forward movement, and yielda'ble means tending to maintain said locking slide in its forward position.

23.- An electrical plug connector according to claim 1, in combination with a. plurality of flat contact blades arranged to carry current supported on the plug, and corresponding receiving contact elements provided on the socket.

HENRY JOHN MODREY.

REFERENCES @ETED The following refierenees are of record in the file of this potent:

Number Number Germany Sept. 15, 1930 

